Method for making cable with a conductive bump array, and method for connecting the cable to a task object

ABSTRACT

A cable with conductive bumps is fabricated by forming a photoresist layer with multiple openings on a cable substrate, coating a conductive layer on the photoresist layer whereby the conductive layer in the openings forms the bumps at circuits on the cable substrate, and then removing the photoresist layer. When connecting the cable to a task object such as an LCD glass substrate or PCB, only a usual non-conductive paste is applied to join the cable and the task object, without use of expensive anisotropic-conductive paste or film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for making a cable with conductivebumps arranged in an array and a method for connecting the cable to anelectronic component, more particularly, the cable can electricallyconnect to the electronic component without need for ananisotropic-conductive paste or film (ACP or ACF).

2. Related Art

Anisotropic-conductive paste (ACP) or anisotropic-conductive film (ACF)has been commonly applied as a major compound for connecting a cable toan integrated circuit (IC) or attaching a circuit board to an LCD glasssubstrate. The major ingredient of the ACP or ACF comprises a greatquantity of small conductive particles contained in glue.

When electrically connecting the LCD glass substrate to the circuitboard by the ACP or ACF through a pressing process, the conductiveparticles will be distributed between the substrate and the circuitboard. For regions where these particles have been pressed, theparticles serve as conductive material between the substrate and thecircuit board. On the contrary, for regions where the particles have notbeen pressed, electrical signals can not be transmitted between thesubstrate and the circuit board even though they are joined together bythe glue.

For example, with reference to FIGS. 6A and 6B, a cable (70) hasmultiple conductive circuits (71) that are electrically connected tosubstrate terminals (not numbered) on a substrate (72) by ACP/ACF (80).The ACP/ACF (80) that contains the conductive particles (81) isdistributed between the cable (70) and the substrate (72). The substrate(72) can be an LCD glass substrate, a printed circuit board etc. For anLCD glass substrate, the substrate terminals can be formed by indium tinoxide (ITO) or metal wires.

With reference to FIG. 7, the ACP/ACF (80) is applied to join terminals(74) of an integrated circuit (IC)(73) to the circuits (71) of the cable(70). The particles (81) that have been pressed in the ACP/ACF (80) alsoserve as material to make an electrical connection between the terminals(74) and the circuits (71).

With reference to FIG. 8, in another embodiment of prior art,non-conductive film or paste (NCF or NCP) (82) is applied to join the IC(73) and the cable (70) together. The terminals (74) of the IC directlycontact the circuits (71) of the cable (70). The disadvantage raised inthis prior art is the unsatisfactory reliability of connection betweenthe IC (73) and the cable (70). If the circuits (71) mis-align with theterminals (74), a defective electrical connection may possibly existbetween cable (70) and the IC (73) because no conductive particles arecontained in the NCF/NCP (82).

Although using the ACP/ACF (80) can solve the drawback of the device inFIG. 8, the ACP/ACF (80) still causes other problems.

1. Specific space is required where the glue of ACP/ACF can flow betweenthe cable and the substrate or IC. However, the conductive particles maythus be unequally distributed due to the flowing motions of the glue.The connecting reliability is then reduced.

2. The width and length of the conductive circuits must be carefullydetermined upon the sizes of the particles, otherwise an undesired shortcircuit or a failed electrical connection between the cable and the taskobject accordingly occur.

3. The fabricating processes of the ACP/ACF are complex.

4. The cost of the ACP/ACF is quite high since only a particularmaterial is suitable for manufacture of the conductive particles.

For the above reasons, a novel cable is proposed to overcome theshortcoming of the prior arts using the ACP/ACF.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a method for makinga cable with conductive bumps, wherein the cable can be electricallyconnected to any task electronic element without use ofanisotropic-conductive paste.

To achieve the objective, the method in accordance with the presentinvention includes the acts of:

-   -   forming multiple conductive circuits on a surface of a cable        substrate;    -   coating a photoresist layer over the multiple conductive        circuits, wherein multiple openings are formed on the        photoresist layer, and some of the openings overlap on the        conductive circuits;    -   forming conductive bumps at the openings that overlap the        conductive circuits so that the conductive bumps protrude from        surfaces of the conductive circuits;    -   removing the photoresist layer from the cable substrate; and    -   coating a protective layer on the conductive bumps.

Further advantages, features and details of the present invention willbe elucidated on the basis of the following description of a preferredembodiment thereof, with reference to the annexed figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view showing a cable in accordance with thepresent invention.

FIG. 1B is a bottom plan view of FIG. 1.

FIG. 2A is a cross-sectional view showing a photoresist layer formed onthe cable in accordance with the present invention.

FIG. 2B is a bottom plan view of FIG. 2A.

FIG. 3A is a cross-sectional view showing conductive bumps are formed onthe cable in accordance with the present invention.

FIG. 3B is a bottom plan view of FIG. 3A.

FIG. 4A is a cross-sectional view showing the cable is electricallyconnected to a task substrate in accordance with the present invention.

FIG. 4B is a top plan view of FIG. 4A.

FIG. 5 is a cross-sectional view showing the cable is electricallyconnected to a task IC in accordance with the present invention.

FIG. 6A is a cross-sectional view illustrating that a cable is mountedto a substrate by ACP/ACF.

FIG. 6B is top plan view of FIG. 6A.

FIG. 7 is a cross-sectional view illustrating that a cable is mounted toan IC by ACP/ACF.

FIG. 8 is a cross-sectional view illustrating that a cable is mounted toan IC by NCP/NCF.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a method to form cable with micro-bumpsarranged in an array configuration. Therefore, the ACP or ACF used inprior art is now not necessary for connecting the cable to a task objectsuch as an LCD glass substrate or a PCB. Since the function of theconventional conductive particles is performed by the micro-bumps, onlythe usual and easily acquired non-conductive paste is used forconnection.

With reference to FIGS. 1A and 1B, multiple conductive circuits (11) areformed on a surface of a cable substrate such as a flexible board or aprinted circuit board (PCB) to construct a cable (10).

With reference to FIGS. 2A and 2B, a photoresist layer (13) withmultiple openings (12) is formed on the same surface over the circuits(11) by a photo mask. Since these openings (12) are arranged in an arrayconfiguration and equally or randomly distributed over the circuits(11), these openings (12) do not need to be purposely formed at specificpositions just over the circuits (11). However, the density of theopenings (12) should be carefully considered upon the lengths or widthsof the circuits (11). Preferably, an included angle approximate 45degrees as indicated by α can be defined by the openings (12) aligned ona line and the circuits. In other words, the random distribution of theopenings (12) can ensure that each circuit (11) has a plurality ofopenings (12) positioned thereon.

With reference to FIGS. 3A and 3B, conductive bumps (14) are formed atthe openings (12) by the electroplating processes or other means. Whenusing the electroplating processes, the conductive bumps (14) arespecifically and exclusively formed at the conductive surface, i.e. atpositions where the openings (12) and the circuits (11) overlap eachother although the remaining openings (12) also experience theelectroplating processes. When the electroplating processes arefinished, the photoresist layer (13) is then removed to expose theconductive bumps (14) protruding from the circuits (11). Theseconductive bumps (14) can then be preferably coated with a protectivelayer consisting of tin, nickel, gold etc. on their surfaces. Therefore,a cable with conductive bumps in accordance with the present inventionis formed. As to the connection between the cable and the LCD glasssubstrate or the PCB, this will be further described hereinafter.

With reference to FIGS. 4A and 4B, the cable (10) having conductivebumps (14) can be attached to the task substrate (72) through thenon-conducting paste (20). The substrate (72) can be an LCD glasssubstrate with conductive terminals formed by ITO or metal wires. Thenon-conducting paste (20) is applied to join the cable (10) and thesubstrate (72) whereby these bumps (14) can electrically contact theconductive terminals on the substrate (72).

With reference to FIG. 5, the non-conducting paste (20) is also appliedto join the cable (10) and an IC (73) whereby these bumps (14) canelectrically contact the conductive nodes of the IC (73).

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size, and arrangement of parts within the principles of the invention tothe fill extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

1. A method for making a cable, the method comprising: forming aconductive circuit on a portion of a cable substrate, another portion ofthe cable substrate being exposed; coating a photoresist layer over theconductive circuit and the exposed cable substrate; forming multipleopenings equally or randomly distributed in the photoresist layer,wherein a first set of the multiple openings overlap the conductivecircuit and a second set of the multiple openings overlap the exposedcable substrate; and forming conductive bumps at the openings thatoverlap the conductive circuit so that the conductive bumps protrudefrom surfaces of the conductive circuit.
 2. The method as claimed inclaim 1, wherein the openings are arranged in an array configuration. 3.The method as claimed in claim 1, wherein the conductive bumps areformed by an electroplating process.
 4. The method as claimed in claim1, further comprising coating a protective layer on the conductivebumps, wherein the protective layer is formed by tin, nickel or gold. 5.A method for connecting a cable having conductive bumps to a task objectwith conductive terminals, the method comprising: forming the cableaccording to claim 1; contacting the conductive bumps on the cable tothe conductive terminals of the task object; and applying non-conductivepaste between the cable and the task object to securely join theconductive bumps and the conductive terminals together.
 6. The method asclaimed in claim 5, wherein the task object is an LCD glass substrate.7. The method as claimed in claim 5, wherein the task object is aprinted circuit board.
 8. The method as claimed in claim 1, wherein anincluded angle defined by the longitudinal direction of the conductivecircuit and the multiple openings aligned on a line is formed.
 9. Themethod as claimed in claim 8, wherein the included angle isapproximately 45 degree.
 10. The method as claimed in claim 1, whereinat least one of the multiple openings concurrently overlaps theconductive circuit and the exposed cable substrate.
 11. The method asclaimed in claim 1, wherein at least one of the conductive bumpsoverhangs the exposed substrate.
 12. A method for making a cable, themethod comprising: forming a conductive circuit on a portion of a cablesubstrate, another portion of the cable substrate being exposed; coatinga photoresist layer over the conductive circuit and the exposed cablesubstrate; forming multiple openings equally or randomly distributed inthe photoresist layer, wherein an included angle defined by thelongitudinal direction of the conductive circuit and the multipleopenings aligned on a line is formed, such that at least one of themultiple openings concurrently overlap the conductive circuit and theexposed cable substrate; and forming conductive bumps at the openingsthat overlap the conductive circuit so that the conductive bumpsprotrude from surfaces of the conductive circuits.
 13. The method asclaimed in claim 12, wherein at least one of the conductive bumpsoverhangs the exposed substrate.